Interpretive Summary: Glyphosate and glufosinate are chemicals registered for use to control weeds in fields planted with transgenic cotton varieties. MSMA is another chemical registered for use on all cotton varieties for control of weeds. Mixing MSMA with glyphosate or glufosinate may help to control some weeds that are difficult to control with glyphosate or glufosinate alone. Weed control was not improved when MSMA was mixed with glyphosate or glufosinate when compared to glyphosate or glufosinate alone. Adding MSMA to glyphosate or glufosinate reduced the level of control of several weed species when compared to control with glyphosate or glufosinate alone. MSMA is not a compatible tank mixture partner with glyphosate or glufosinate for weed control in cotton.

Technical Abstract:
Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5x, 1x, and 2x rates, with 1x rates of 0.84 kg ae/ha, 0.5 kg ai/ha, and 2.2 kg ai/ha, respectively. Glyphosate and glufosinate provided similar levels of control of most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared to either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2x rate of either herbicide alone. MSMA is not a compatible tank mixture partner with glyphosate or glufosinate for weed control in cotton.